Separator made of a fibrous porous material such as a felt

ABSTRACT

A separator is made of a porous material and is intended to treat gaseous effluents which contain particles whose size is substantially less than one micrometer or of the order of one micrometer. The porous material includes channels. The channels are delimited by a fibrous porous material such as batting.

FIELD OF THE INVENTION

The present invention relates to the field of separators and morespecifically to means intended to separate particles, in solid or liquidform, from a gaseous stream and whose size is less than or of the orderof one micrometer.

BACKGROUND OF THE INVENTION

Many methods and devices have already been disclosed to that end.

U.S. Pat. No. 5,626,651 describes a method and a system of this typeaccording to which the turbulent gaseous stream flows above a series ofplates which define non-turbulent zones in which the particles aretrapped. More precisely, the plates are parallel to one another andvertical. A filtering means consisting of fibers can also be providedbetween said plates in order to improve filtration of the finerparticles notably.

International patent application WO-95/28,217 describes a device basedon the same principle, but where the plates are provided with slots orreplaced by grates.

Furthermore, patent application WO-97/00,102 relates to a separatorarranged at the exhaust of Diesel type engines in order to collect theparticles contained in the exhaust gas.

A honeycomb structure is therefore pierced with channels perpendicularto the opening of the honeycomb cells, this structure having a porosityof the order of 70%.

However, it has been observed that this type of separator cannot be usedfor fogs because the droplets trapped in the material cannot be removedby drainage.

International patent application WO-97/27,928 relates to a separatorprovided with one or more vertical flow channels laterally delimited byfibrous corrugated elements.

In this document, an agglomerator is necessarily arranged upstream fromthe separator in order to have larger particles likely to be separatedin the separator. This is therefore relatively expensive and involvespressure drops that are by no means insignificant.

In U.S. Pat. No. 5,626,651, the trapped particles accumulate on thewalls, then fall under the effect of gravity onto the bottom of thedevice. Means intended to shake the walls are often required to causethese particles accumulated on the walls to fall down.

This device poses problems when very fine particles, smaller than onemicrometer, are to be separated. In this case, the height of the flowchannel must be very small and therefore the height of the plates verylarge so that the equipment is quite bulky for a very small section offlow. The same problem exists in the device according to documentWO-95/28,217.

However, these known means do not allow to collect and to removeefficiently particles in liquid or solid form whose size is less thanabout one micrometer.

Patent application WO-99/19,044 published in the name of the applicantdescribes a separator made of a foam comprising channels intended forthe turbulent flow of the gaseous effluents, which allows to overcomethe aforementioned drawbacks.

However, the applicant has continued research in the sphere ofseparation and has been able to develop a device which significantlyimproves the separation of very small particles present in gaseouseffluents.

In a first research stage, it has been observed that, when a gaseouseffluent in the turbulent state containing suspended particles flowsthrough a channel 2 of diameter D made from a porous material (see FIG.1), the boundary layer of this effluent enters, from the peripheral edgedelimiting this channel, the inside of the porous material over athickness L of a peripheral stratum 3 and, as a result of the eddygenerated by this effluent, the particles are carried into this stratum3 where they are collected by the fibers of the pores of the porousmaterial.

Channel 2 therefore remains free of any hindrance, which allows thegaseous effluent to flow all along the channel with a constant pressuredrop and flow rate since the accumulation of the particles collectedlies in an annular space surrounding this channel.

According to the same principle and during another research stage, ithas been discovered that, when a gaseous effluent in the turbulent statecontaining suspended particles flows along a face of a porous materialin form of a sheet, the boundary layer of this effluent moves towardsthe inside of the porous material and, by means of the turbulent eddygenerated by this effluent, the particles are carried into thesuperficial layer of this sheet where they are collected by the fibersof the pores of the porous material.

Similarly, in this configuration, the pressure drop of the effluent isminimal since the particles have accumulated in the body of the sheetwithout hindering the flow of this effluent.

SUMMARY OF THE INVENTION

The present invention thus relates to a separator made of a porousmaterial, intended to treat under optimum conditions gaseous effluentscontaining liquid or solid particles whose size is substantially lessthan one micrometer or of the order of one micrometer.

According to the invention, a separator made of a porous materialintended to treat gaseous effluents containing particles whose size issubstantially less than one micrometer or of the order of one micrometerand comprising channels is characterised in that the channels aredelimited by a fibrous porous material such as batting.

The porosity of said material can range between 90% and 99%.

The size of the pores forming said material can range between about 0.1mm and about 5 mm.

The diameter of the fibers forming said material can range between 2 μmand 100 μm.

The diameter of the channels running through said material can rangebetween 3 and 15 mm.

The length of the channels can range between about 10 cm and about 200cm.

The effluents can flow in the turbulent state from one end of thechannels to the other.

The material of the fibers can be a synthetic material.

The material of the fibers can be a ceramic material.

The porous material can have the shape of a sheet comprising channels.

The thickness of the sheet can range from 1 to 10 mm.

The porous material can be obtained by piling sheets.

The sheet can be supported by a plate made from an impermeable materialhaving the same surface area as the sheets and provided with holescorresponding to the channels of the sheets.

The sheets are arranged at a distance from one another by bracing means.

The invention also relates to a separator made of a porous materialintended to treat gaseous effluents containing particles whose size issubstantially less than one micrometer or of the order of one micrometerand comprising channels, characterised in that it comprises at least onemodule consisting of at least one sheet made of a porous material,comprising channels and arranged substantially parallel to and at adistance from at least one other sheet and in that it comprises at leastone plate made from an impermeable material having the same surface areaas said sheet and provided with holes corresponding to the channels ofthe sheets.

The porosity of said material can range between 90% and 99%, the size ofthe pores ranges between about 0.1 mm and about 5 mm, and the diameterof the channels ranges between 3 and 15 mm.

The effluents can flow in the turbulent state over at least one face ofthe sheet.

The module can comprise at least two subassemblies of at least twosheets arranged at a distance from one another.

The sheets can be arranged at a distance from one another by bracingmeans.

The bracing means can consist of a frame preferably obtained from theplate.

The porous material can be charged with static electricity.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features, advantages and improvements according to the inventionwill be clear from reading the description hereafter, given by way ofnon limitative example, with reference to the accompanying drawingswherein:

FIG. 1 is a large-scale cross-sectional view of a channel of aseparator,

FIG. 2 is a perspective view of part of a separator according to theinvention,

FIG. 3 is a diagrammatic longitudinal section of a device according tothe invention,

FIG. 4 is a perspective view of another embodiment of the invention,

FIG. 5 is a view with local cross-sections showing a variant of theinvention,

FIG. 6 is a perspective view showing another variant of the invention.

DETAILED DESCRIPTION

FIG. 2 shows a body 1 of a separator consisting, according to theinvention, of a fibrous porous material such as batting.

Of course, batting is understood to be a porous material consisting offibers or threads intimately entangled without weaving or spinning.

The material used for the fibers can advantageously be a syntheticmaterial such as polyester or polypropylene, or a ceramic material.

The porous materials used in the invention consist of small pores, theirporosity ranging between 90 and 99%.

The size of the pores ranges between about 0.1 mm and about 5 mm, andthe diameter of the fibers ranges between 2 μm and 100 μm, but afilament diameter ranging between 2 and 20 μm may sometimes bepreferred.

Furthermore, as can be seen in this figure, channels 2, preferablyparallel to one another, are pierced or drilled in the body made offibrous porous material or batting 1 and allow a fluid to flowtherethrough as shown by arrows A in FIG. 2.

The diameter of channels 2 ranges here between 3 and 15 mm, and thedistance between two channels can range between about 3 mm and up toabout 20 mm.

The cross section occupied by flow channels 2 is between 15 and 50% ofthe total cross section of said body.

The section of the channels is preferably circular, as illustrated inFIG. 2, but the sections of the channels may have another shape withoutdeparting from the scope of the invention.

The general layout of the channels can be such that a gridded network ofparallel channels is formed, but a network of channels with a differentlayout can be considered without departing from the scope of theinvention.

By way of example, a test has been carried out to separate liquidparticles, here droplets contained in an oil fog, by passage through abody made of polyester batting consisting of about 15-μm diameter fibersand having a 97% porosity, which allowed to obtain a 99.5% particlerecovery ratio.

Another test has been carried out in order to separate dropletscontained in the same oil fog with a body made of ceramic battingcomprising about 2-μm diameter fibers and having a 93% porosity, whichallowed to obtain a 99.8% recovery ratio for said droplets.

The tests carried out have allowed to show that the thickness L ofstratum 3 (see FIG. 1 ) of the peripheral edge of channel 2 is directlyproportional to the diameter (Df) of the fibers and to the diameter (D)of channel 2, that the value of ratio L/Df×D is substantially equal to aconstant and that the value of L substantially ranges between 5 and 10times the diameter of the pores.

In the field of separation of droplets forming a fog, the presentinvention has the advantage of draining the droplets which thus form aliquid that flows through gravity through the batting body.

An application example is illustrated by FIG. 3, which relates to adevice provided with a viscous fog separator.

A mixture of gas and oily fog is fed, as shown by arrow B in FIG. 3,into an enclosure 4 which contains body 1 made of a porous battingmaterial.

The mixture flows through channels 2 pierced substantially horizontalthrough body 1 and flows out of enclosure 4 as shown by arrow C at theother end of channels 2 after the oil droplets contained in this foghave settled in said channels. Drainage of the liquid formed after thedroplets have settled, as obtained according to the invention, allowsthe oil to be collected at the bottom of enclosure 4. This oil can bedischarged and stored in a tank or any specific means such as the meansshown by reference number 5.

Thus, the oil collected by the threads or the fibers forming the battingflows to the bottom of the device substantially at the same flow rate asits absorption rate.

In relation to known separators, the present invention allows to dowithout a carcass or another holding element since the batting isoriginally rigid enough to be perforated by any means known in the art.Furthermore, a high precision can be obtained when making the channels.

The device according to the invention is also suited to the separationof gaseous effluent fumes because the deposits then appear on thethreads or fibers of the batting where they form a solid or bituminouslayer.

The particles being present in low concentrations, cleaning and/orreplacement of the batting is rarely required.

Cleaning is performed, for example, during operations intended tovibrate or to shake the batting so that the particles contained thereincan be discharged and then collected by any known means.

Furthermore, without departing from the scope of the invention, thebatting according to the invention can be washed when it is dirty andput back in place once clean.

The separator according to the invention is also suited to theseparation of industrial dust.

A test has been carried out in the case of separation of fumes fromexhaust gas of a Diesel engine, with a batting body having 2-μm diameterceramic fibers.

The section of this body is 8 cm by 10 cm, it is 25 cm in length andprovided with 54 substantially circular 5-mm diameter channels.

During the test, the rate of flow of the exhaust gas was 100 m³/h andthe pressure drop was 8 kPa, and 80% of the soot present in this gascould be collected.

Another test has been carried out with dust contained in ambient air,for which the results were particularly satisfactory with a recoveryratio of the order of 82% for particles with a diameter below 0.5 μm.

This test was carried out using a separator consisting of a batting bodymade of 20-μm diameter polypropylene fibers charged with staticelectricity.

This separator had a section of 11 cm by 25 cm and a length of 23 cm,and it was provided with 181 5.5-mm diameter circular channels.

The rate of flow of the air through the separator was about 70 m³/h,with a pressure drop of about 0.25 kPa.

In an embodiment of the invention as illustrated in FIG. 4, channels 2are obtained by piling up sheets 11 made of a fibrous porous materialsuch as synthetic material batting with a 97% porosity and fiberdiameters of the order of 15 μm, said pile forming body 10 of theseparator.

These parallelepipedic sheets, preferably identical, with a thickness ofabout 0.95 cm and a section of 11 cm by 25 cm, are each pierced with 123holes or channels about 9.5 mm in diameter, then piled up 30 in numberand arranged crosswise to the direction of a gaseous effluent in anabout 30.5-cm long housing so as to form a multi-sheet block thuscomprising, as a result of piling, 123 9.5-mm diameter channels.

The tests carried out with this multisheet block allowed to obtain adroplet recovery ratio of the order of 99.5% with a pressure drop of 2.5kPa (10 in.w.c.) and a rate of flow of 250 m³/h (150 CFM) of an oil fogcontaining droplets of a diameter below 1 μm.

Preferably, the batting sheets can be stiffened further by means of aspecific treatment that will reinforce the cohesion of the fibers.

By way of example, this treatment consists in dipping the sheets, forexample made of ceramic batting, in a n-decane silane solution, then inremoving the excess solution on and in these sheets, in drying them withwarm air and in subjecting the silane in an oven to a pyrolysisgradually up to 400° C.

In a variant of the invention, the separator comprises a pile of atleast one module consisting of at least one sheet 11 made of a porousmaterial, which is held at a distance from at least one other sheet, ascan be seen in FIG. 5, while being arranged substantially crosswise tothe direction of the gaseous effluent from B to C.

In this case, the porous material used can be a foam, batting or clothof high porosity ranging between 90% and 99%.

Then, after forming sheets with holes or channels, as described above,an orifice 12 is to be pierced in the vicinity of each corner of thesheets, then sheets held at a distance in relation to one another bybraces 13, here tubular cylindrical braces arranged in agreement withorifices 12, are to be piled up.

Once this piling operation completed, a tie bar 14 is slid throughorifices 12 and tubular braces 13 so as to run through the whole of thepile, then this assembly is held in position by locking means such asBelleville type lock spring washers 15 arranged at each free end of eachtie bar.

A rigid block is thus obtained, consisting of substantially parallelsheets 11 arranged at a distance from one another, and wherein holes orchannels 12 of each sheet are the continuation of the holes of the nextsheet.

Preferably, as shown in FIGS. 4 and 5, at least one face of at least onesheet 11 is to be provided with a support means 16 forming a stiffeningmeans for the sheet on which it rests and a line for the gaseouseffluent flowing through said sheet.

Preferably, this support means is arranged downstream from each sheet 11in relation to the direction of flow of the gaseous effluent shown bythe arrows in these figures, and it is arranged opposite and preferablyin contact with the back face of the sheet, the front face being theface which faces the gaseous effluent.

This support means consists of a thin rigid plate made of an impermeablematerial 16 such as a cardboard, metal or plastic plate, having the samesurface area as the sheets and through which are pierced holes andorifices corresponding to the holes or channels 2 and orifices 12 of thesheets.

Preferably, the diameter of the holes of plate 16 is slightly largerthan the diameter of the holes provided on sheets 11.

Thanks to the presence of this plate, the gaseous effluents cannot flowthrough all of the sheet and they are forced to flow through channels 2.

Of course, without departing from the scope of the invention, it is alsopossible to separate by means of free spaces subassemblies of at leastone sheet so as to obtain a series of at least two subassemblies ofsheets with a fixed or variable number of sheets, as shown in FIG. 6with a succession of subassemblies of two sheets, each subassembly beingseparated by spaces.

In this layout, all or part of the subassemblies of sheets can beprovided on their downstream face with a plate 16 as described above.

In a series of tests relative to the variant corresponding to FIG. 5,which is applied to remove particles present in the exhaust gas of aDiesel engine, ceramic batting sheets with extremely fine fibers, suchas those marketed under the trade name Kaowool® S, are used. Each sheetis 6-mm thick and is supported by a perforated metal plate that is about3 mm thick and preferably riveted to the batting sheet. The holes orchannels provided in the sheet, which correspond to those of the metalplate, are about 5 mm in diameter and arranged in a triangularconfiguration so that the distance between each center and the holes isabout 8 mm. Each sheet is separated from the neighbouring sheet by adistance ranging between 10 mm and 50 mm, preferably of about 12 mm.

To carry out these tests, ten 300-mm diameter sheets comprising 12005-mm diameter holes or channels were arranged in a cylindrical case andit has been observed that almost all of the particles had been removedfor exhaust gases having a velocity ranging between 30 m/s and 100 m/s.

In order to free the sheets from the particles they contain and toprevent their saturation, these sheets are to be regenerated byoxidation.

Advantageously, a lattice is arranged on the front face of the sheet,and it is connected to the sheet and to the plate by riveting asdescribed above. This lattice, associated with the plate, has theadvantage of reinforcing the resistance of the batting sheet to stressesdue to the velocity of the gas and/or to vibrations.

In another experimental run relative to the variant illustrated in FIG.6, the separator consists of a multiplicity of polypropylene sheetswhich are 11 cm by 25 cm in dimensions and 1.5 mm in thickness, withabout 20-μm diameter fibers permanently charged with static electricity.Each sheet is provided with 6-mm diameter holes or channels and it isseparated from the others by a distance that is approximately 3 to 10times the diameter of the holes and, in the case of this test, thedistance is 20 mm, preferably with a triangular layout so as to obtainabout 181 holes or channels.

The back face of each sheet, i.e. the opposite side in relation to thegaseous effluent, is provided with a 0.75-mm thick perforated aluminiumplate on which the sheet is advantageously stuck, for example by gluing,and whose holes correspond to those of the sheet.

Preferably, each edge of the metal plate is folded up by about 90° in anopposite direction to that of the sheet so as to form a rigid frameserving as bracing means for two neighbouring sheets in order toseparate them by a distance of preferably about 22 mm.

For this test, the separator comprises a module consisting of a pile of19 sheet blocks charged with static electricity and containing each 2piled sheets of equal size and hole arrangement, each block beingseparated from the other by a 22-mm space, the holes of each sheet beingcarefully arranged in line. This module is housed in a case open at bothends, whose outlet end is connected to a suction unit whereas the inletend communicates with the gaseous effluent that is sucked through thechannels by the suction unit.

It is possible to have only one plate on the back face of the lastsheet, in relation to the direction of flow of the gaseous effluent.

During this test, the gaseous effluent has a rate of flow of about 70m³/h, with a pressure drop of 0.25 kPa, and the particle recovery ratiois of the order of 82%.

Of course, several sheet block modules arranged one after the other canbe housed in the same case so as to form a device intended to separatethe particles contained in a gaseous effluent.

In the case of FIGS. 5 and 6, the gaseous effluent is in turbulent formupstream from each sheet or each block of sheets. More particularly, thegaseous effluent flowing out of a sheet or block of sheets ends in theturbulent state in the space between two sheets or blocks of sheets.Because of these turbulences, the ultrafine particles hit, as a resultof the turbulent deposition mechanism, the front surface of the sheetsurrounding the holes or channels and they are collected by the fibersof this sheet with the help of the electrostatic forces.

In addition, particles can also be collected by the stratum of the holesformed in the sheets or the blocks of sheets as described in particularin connection with FIGS. 1 and 2.

It can be observed that, by using a distant-sheet separator, a quitesignificant material gain is obtained in relation to a block consistingof piled sheets as shown in FIG. 4.

By way of example, in order to obtain the same particle recovery withthe same pressure drop and the same velocity of flow of the gaseouseffluent as in the embodiment of FIG. 5, it would be necessary to use ablock consisting of about 500 piled sheets.

Thus, the embodiment of FIG. 5 allows to obtain a material saving higherthan 90% in relation to that of FIG. 4.

The present invention is not limited to the examples described above andit includes any variant.

The channels may notably consist of an assembly of batting sheetsforming a grid pattern through which the effluents to be treated flow.

1. A separator made of a porous material, intended to treat gaseous effluents containing particles whose size is substantially less than one micrometer or of the order of one micrometer, and comprising channels, wherein the channels are delimited by a fibrous porous material in form of at least one sheet comprising the channels extending therethrough, wherein the at least one sheet is supported by a plate made of an impermeable material having the same surface area as the at least one sheet and provided with holes corresponding to the channels of the at least one sheet.
 2. A separator as claimed in claim 1, wherein the porosity of said material ranges between 90% and 99%.
 3. A separator as claimed in claim 1, wherein the size of the pores forming said material ranges between about 0.1 mm and about 5 mm.
 4. A separator as claimed in claim 1, wherein the diameter of the fibers forming said material ranges between 2 μm and 100 μm.
 5. A separator as claimed in claim 1, wherein the diameter of channels running through said material ranges between 3 and 15 mm.
 6. A separator as claimed in claim 1, wherein the length of channels ranges between about 10 cm and about 200 cm.
 7. A separator as claimed in claim 1, wherein the effluents flow in the turbulent state from one end of channels to the other end.
 8. A separator as claimed in claim 1, wherein the material of the fibers is a synthetic material.
 9. A separator as claimed in claim 1, wherein the material of the fibers is a ceramic material.
 10. A separator as claimed in claim 1, wherein the thickness of sheet ranges between 1 and 10 mm.
 11. A separator according to claim 1, wherein the fibrous porous material is made by piling up a plurality of sheets.
 12. A separator as claimed in claim 11, wherein the sheets are arranged at a distance from one another by bracing means.
 13. A separator as claimed in claim 1, wherein the porous material is charged with static electricity.
 14. A separator as claimed in claim 1, wherein the fibrous porous material comprises batting.
 15. A separator according to claim 1, wherein the channels extend in a flow direction of the gaseous effluents.
 16. A separator made of a porous material, intended to treat gaseous effluents containing particles whose size is substantially less than one micrometer or of the order of one micrometer, and comprising channels, wherein the separator comprises at least one module having at least one sheet made of a fibrous porous material, comprising channels therethrough and arranged substantially parallel and at a distance from at least one other sheet, comprising channels therethrough and at least one made of an impermeable material having the same surface area as each sheet and provided with holes corresponding to channels of sheets.
 17. A separator as claimed in claim 16, wherein the porosity of said material ranges between 90% and 99%, the size of the pores ranges between about 0.1 mm and about 5 mm, and the diameter of channels ranges between 3 and 15 mm.
 18. A separator as claimed in claim 16, wherein the effluents flow in the turbulent state over at least one face of sheet.
 19. A separator as claimed in claim 1, wherein the module comprises at least two subassemblies of at least two sheets arranged at a distance from one another.
 20. A separator as claimed in claim 16, wherein the sheets are arranged at a distance from one another by bracing means.
 21. A separator as claimed in claim 20, wherein the bracing means consist of a frame.
 22. A separator as claimed in claim 21, wherein the frame is obtained from the plated. 